Adult articular cartilage has been found to actually contain a small population of resident stem cells that have a restricted differentiation potential: these cells become permanent chondrocytes when placed in exactly the same conditions under which MSCs become endochondral chondrocytes. What makes the differentiation pathway for these resident stem cells different from MSCs, and seemingly all other stem cells for which chondrogenesis has been tested? We hypothesize that the lineage restriction of articular cartilage stem cells (ACSCs) is driven by differences in RNA expression. The specific aim to test this hypothesis is to define the differences in the transcriptomes between articular cartilage stem cells and mesenchymal stem cells and the permanent and endochondral chondrocytes they differentiate into. Next generation RNA sequencing techniques will be used to compare the transcriptomes of ACSCs and MSCs and the transcriptomes of the chondrocytes differentiated from these two stem cell types. Pathways that control the differential differentiation of ACSCs and MSCs will be identified. The analysis will include microRNAs and we aim to identify those involved in the regulation of the differentiation potential of the two stem cell types as well as permanent and endochondral chondrocyte differentiation. There are presently no markers that define the ACSC population. Although several groups have suggested cell surface markers can define ACSCs, these have not been rigorously examined. To-date, no comprehensive screen for markers has been conducted. We hypothesize that a combination of markers can be determined for the ACSC population in the manner done for other stem cell types. Surface marker array technology will be used to search for a combination of markers that can be used to define the ACSC population. Such markers can then be used to efficiently isolate permanent cartilage-producing stem cells for tissue engineering, and assess the level of stem cells in different stages of cartilage pathologies.